Linux is a clone of the Unix kernel, written from scratch by Linus Torvalds with assistance from a loosely-knit team of hackers across the Net. It aims towards POSIX and Single UNIX Specification compliance. It has all the features you would expect in a modern fully-fledged Unix kernel, including true multitasking, virtual memory, shared libraries, demand loading, shared copy-on-write executables, proper memory management, and TCP/IP networking.

G4L is a hard disk and partition imaging and cloning tool. The created images are optionally compressed, and they can be stored on a local hard drive or transferred to an anonymous FTP server. A drive can be cloned using the "Click'n'Clone" function. G4L supports file splitting if the local filesystem does not support writing files larger than 2GB. The included kernel supports ATA, serial-ATA, and SCSI drives. Common network cards are supported. It is packaged as a bootable CD image with an ncurses GUI for easy use.

Recovery Is Possible (RIP) is a CD or USB
boot/rescue/backup/maintenance system. It has
support for many filesystem types (Reiserfs, Btrfs, Ext2/3/4, HFS+, ISO-9660, Squashfs, UDF, XFS, JFS, UFS2, CIFS, MS DOS, NTFS, and VFAT) and contains several utilities for system recovery. It also has IDE/SCSI/SATA, RAID, LVM2, and Ethernet/Wireless network support.

Slackware is the longest-running distribution of the Linux operating system. Slackware offers a stable and secure version of Linux that is perfect for home, office, or educational use. Slackware is easy for beginners to install, but contains all the advanced features required by the experienced UNIX power-user.

CentOS is an enterprise Linux distribution based
on the sources from Red Hat Enterprise Linux.
CentOS conforms with Red Hat's redistribution
policy and aims to be 100% binary compatible. Each
CentOS version is supported for 7 years (by means
of security updates). A new CentOS version is
released every 2 years and each CentOS version is
regularly updated (every 6 months) to support
newer hardware. Currently, there are 4 different
supported CentOS releases: CentOS-5 is based on
Red Hat Enterprise Linux 5, CentOS-4 is based on
RHEL4, CentOS-3 is based on RHEL3, and CentOS-2 is
based on RHAS2.1.

Debian is an operating system for your computer that consists only of Free Software. It uses the Linux kernel, and a large part of the basic tools that fill out the operating system come from GNU, which are also free. It comes with thousands of packages.

Nuttx is a real-time embedded operating system (RTOS). It has a small footprint that is usable in micro-controller environments. It is fully scalable from tiny (8-bit) to moderate embedded (32-bit) systems. It also aims to be fully compliant to standards, to be fully real time, and to be totally open.

SystemRescueCd is a Linux system available from a bootable CDROM
that provides an easy way to perform administrative tasks on your
computer, such as creating and editing the partitions of the hard disk
or backing up data. It contains a lot of system utilities (such as
parted, partimage, and fstools), and basic programs (such as editors,
midnight commander, and network tools). It also includes GParted, a
Partition Magic clone that makes editing partitions easy with its
graphical user interface. This CDROM aims to be very easy to use and
accessible to everybody, and it also provides advanced personalization
features.

Tor-ramdisk is a uClibc-based micro Linux distribution whose only purpose is to host a Tor server in an environment that maximizes security and privacy. Tor is a network of virtual tunnels that allows people and groups to improve their privacy and security on the Internet. Security is enhanced in tor-ramdisk by employing a monolithically compiled GRSEC/PAX patched kernel and hardened system tools. Privacy is enhanced by turning off logging at all levels so that even the Tor operator only has access to minimal information. Finally, since everything runs in ephemeral memory, no information survives a reboot, except for the Tor configuration file and the private RSA key, which may be exported and imported by FTP or SSH.